Two substudies are included in Part I of the study: 1) a medical imaging substudy to evaluate changes in brain amyloid protein load using positron emission tomography (PET) and an amyloid tracer ([18F]flutemetamol); and 2) a cerebrospinal fluid (CSF) biomarker substudy to evaluate changes in CSF concentrations of amyloid-β related peptides, total tau, and phosphorylated tau (p-tau). The substudies will be conducted only at designated investigational sites. Participants are not required to take part in a substudy in order to take part in the larger trial.